Canine adrenal glands served as a model to study neurotransmitter release elicited by GABA receptor stimulation. Infusion of GABA or GABA-mimetics in the adrenal gland increased the release of catecholamines and met-enkephalin-like peptides. This release was a consequence of direct depolarization of chromaffin cell membranes and was not mediated transsynaptically through acetylcholine or met-enkephalin.